l ‐GLUTAMATE AND GLUTAMINE IMPROVE HAEMODYNAMIC FUNCTION AND RESTORE MYOCARDIAL GLYCOGEN CONTENT DURING POSTISCHAEMIC REPERFUSION: A RADIOACTIVE TRACER STUDY IN THE RAT ISOLATED HEART

SUMMARY1 l ‐Glutamate and glutamine have been suggested to have cardioprotective effects. However, the issue is controversial and the metabolic mechanisms underlying a beneficial effect are not well understood. 2 In the present study we investigated the effects of l ‐glutamate and glutamine on haemodynamic recovery, the rate of de novo glycogen synthesis and myocardial glucose uptake during postischaemic reperfusion. 3 .  Hearts from male Wistar rats (250–300 g) were divided into three groups as follows: (i) control ( n  = 12); (ii) l ‐glutamate ( n  = 12); and (iii) glutamine ( n  = 12). Hearts were mounted in a Langendorff preparation and perfused with oxygenated Krebs’–Henseleit solution at 80 mmHg and 37C. Global ischaemia for 20 min was followed by 15 min reperfusion, during which l ‐glutamate (50 mmol/L) or glutamine (20 mmol/L) were administered. Left ventricular developed pressure (LVDP), de novo synthesis of glycogen using [ 14 C]‐glucose and myocardial glucose uptake using d ‐[2‐ 3 H]‐glucose were measured. 4 l ‐Glutamate and glutamine increased postischaemic LVDP ( P <  0.01 vs control hearts for both). l ‐Glutamate and glutamine increased de novo glycogen synthesis by 78% ( P <  0.001) and 55% ( P <  0.01), respectively. At the end of reperfusion, total myocardial glycogen content was increased by both l ‐glutamate and glutamine (5.7 ± 0.3 and 6.2 ± 0.7 mmol/g wet weight, respectively; P  < 0.05 and 0.01, respectively) compared with that in control hearts (3.6 ± 0.4 mmol/g wet weight). Neither l ‐glutamate nor glutamine affected myocardial glucose uptake during reperfusion. 5 .  Improved postischaemic haemodynamic recovery after l ‐glutamate and glutamine supplementation during reperfusion is associated with increased de novo glycogen synthesis, suggesting a favourable modulation of intracellular myocardial carbohydrate metabolism.